The present invention relates to a superconducting wire and a method of manufacturing the same and, more particularly, to a superconducting wire which exhibits an enhanced critical current density and a method of manufacturing the same.
Intermetallic compounds such as Nb.sub.3 Sn and Nb.sub.3 Ge are known as superconducting materials and are put into practical use. However, the critical temperature (Tc) at which the superconductive state of these intermetallic compounds is attained is, for example, 23.degree. K. even in the case of Nb.sub.3 Ge which has the highest Tc among the intermetallic compounds of the above-mentioned type. This has made it necessary for them to be cooled by means of liquid helium.
In 1987, it was found that oxides expressed as YBa.sub.2 Cu.sub.3 O.sub.7-.delta. possess a Tc, about 90.degree. K. which is tremendously higher in comparison with those of the intermetallic compounds conventionally known as superconductive materials. Since the Tc of such superconducting oxide materials is much higher than the boiling point (77.degree. K.) of liquid nitrogen, they can be cooled by means of inexpensive liquid nitrogen, thus making it unnecessary to use very expensive liquid helium.
Because the conventionally known superconducting materials are metals, they can be formed into wires relatively easily by, for instance, wire drawing. In contrast, because superconducting oxide materials are ceramics, they possess poor levels of ductility, thus making it very difficult to form them into wires. To cope with this problem, a wire-forming method has been devised and was reported in the MRS Spring Meeting, 1987 (pages 219-221). This method comprises filling a pipe with a superconducting oxide powder, drawing the resultant body, and, thereafter, subjecting the drawn body to heat treatment. With this method, however, since a powder is charged into a pipe in order to allow the superconducting oxide material to be formed into a wire, the areas of contact between particles forming the superconductive powder are small. Thus, a high critical current density Jc cannot be achieved. In addition, because the particles of a superconducting oxide material have a perovskide layer structure, current flows therein anisotropically. The reported method gives no consideration to this anisotropy. As a result, depending upon the orientation in which the bonding of the particles occurs, the level of current flowing therein is apt to be reduced with the result that it has been impossible to obtain a high Jc.